A known position sensorless vector control method is disclosed in Patent Document 1, in which error between an estimated phase value θc* relative to a control axis and a phase value θ of a permanent magnet motor is estimated from a calculation (this error will be referred to below as the axial error Δθ).
In the disclosed method, commanded voltage values (Vdc*, Vqc*), which are outputs in vector control, detected current values (Idc, Iqc), and a commanded speed value (ω1c) are used to estimate the axis error from a calculation in equation (1).
                    [                  Equation          ⁢                                          ⁢          1                ]                                                                      Δ          ⁢                                          ⁢          θ          ⁢                                          ⁢          c                =                              tan                          -              1                                ⁡                      [                                                            Vdc                  *                                -                                                      R                    *                                    ·                  Idc                                +                                                      ω                    1                                    ⁢                                      c                    ·                                          Lq                      *                                        ·                    Iqc                                                                                                Vqc                  *                                -                                                      R                    *                                    ·                  Iqc                                -                                                      ω                    1                                    ⁢                                      c                    ·                                          Lq                      *                                        ·                    Idc                                                                        ]                                              (        1        )            
Where
Vdc*: d-axis commanded voltage value
Vqc*: q-axis commanded voltage value
Idc: d-axis detected current value
Iqc: q-axis detected current value
R: Value obtained by the addition of the winding resistance of a motor to the wire resistances of a motor and electric power converter
Ld: d-axis inductance value
Lq: q-axis inductance value
Ke: Induced voltage constant
*: Setting
To generate the estimated phase value θc*, the estimated speed value ω1c is controlled so that the estimated axis error Δθc becomes θ and integration is performed.
Patent Document 1: Japanese Patent Laid-open No. 2001-251889